The health system could reach a crisis level with the system "overwhelmed" with people needing to be treated for diseases such as type 2 diabetes, he said. "It could end up needing to be a user pay system."

Advances in technology and changes in nutrition had contributed to people's waistlines expanding, Mr Hill said.

"I don't think people eat particularly well -- I think there's a lack of education.

"People don't know what a portion size is, they don't know that half your plate should be vegetables, a quarter of your plate should be carbohydrates and a quarter of your plate needs to be protein."

Auckland University's department of paediatrics' senior research fellow John Thompson said the figures were shocking, but the high rates had been known for a while now.

"There have been a number of intervention programmes trialled all over the place, but the problem is nobody has come up with one that seems to have worked long term," he said.

Parents needed to take responsibility for the food that was served to their children and how active their kids were.

"If the parents are eating badly then that's what the children are eating as well."

There situation has reached a crisis point, Dr Thompson said.

"If you look at the rates of obesity and cardio-vascular disease in the population, they are just exploding."

It was difficult for overweight children to shed the weight if they had not done so by about 5 years old, Dr Thompson said.

"My message for parents would be keep the kids active, limit their time in front of the TV and make sure they're eating healthily -- pretty simple."

Dr Carol Wham from Massey University's Institute of Food, Nutrition and Human Health said there was a "real worry" in the nutrition community about both a lack of physical activity and exposure to processed and fast foods.

The research, published in medical journal The Lancet, was conducted by an international consortium of researchers led by the Institute for Health Metrics and Evaluation (IHME) at the University of Washington.

It was part of the wide-ranging Global Burden of Disease project.

The study found that obesity rates in developed countries had slowed since 2006, but in developing countries -- where almost two-thirds of the world's obese people live -- increases looked likely to continue.

Key NZ findings:

* About 2.2 million adults in New Zealand are overweight, and of those 960,000 are obese.

* Within the Australasia region, New Zealand has the highest rate of obesity in both adults (29 per cent) and children (9 per cent).

* More women than men are obese, with 510,000 women falling into that category compared to 450,000 men.

* Half of all overweight women in New Zealand are obese.

* 30 per cent of women aged 20 or older are obese, more than triple the obesity rates among girls (9 per cent).

* Obesity rates among boys climb from about 10 per cent in childhood and adolescence to almost 28 per cent in adulthood.

Key global findings:

• 2.1 billion people - nearly 30 per cent of the world's population - are overweight or obese.• The number of overweight and obese individuals in the world has increased from 857 million (20 per cent) in 1980, to 2.1 billion (30 per cent) in 2013.• In high-income countries, some of the largest increases in adult obesity have been in the US (where one-third of adults are obese), Australia (where nearly 30 per cent of men and women are obese), and the UK (where around a quarter of the adult population is obese).• More than 50 per cent of the world's 671 million obese live in 10 countries (ranked beginning with the countries with the most obese people): US, China, India, Russia, Brazil, Mexico, Egypt, Germany, Pakistan, and Indonesia.- The highest proportion of the world's obese people (13 per cent) live in the US.